1. Field of the Invention
The invention relates generally to methods and apparatus for dispensing a viscous material on a substrate, such as a printed circuit board, and more particularly to a method and an apparatus for dispensing material on a substrate with enhanced efficiency.
2. Discussion of Related Art
There are several types of prior art dispensing systems used for dispensing precise amounts of liquid or paste for a variety of applications. One such application is the assembly of integrated circuit chips and other electronic components onto circuit board substrates. In this application, automated dispensing systems are used for dispensing dots of liquid epoxy or solder paste, or some other related material, onto circuit boards. Automated dispensing systems are also used for dispensing lines of underfill materials and encapsulents, which may be used to mechanically secure components to the circuit board. Exemplary dispensing systems described above include those manufactured and distributed by Speedline Technologies, Inc. of Franklin, Mass.
In a typical dispensing system, a pump and dispenser assembly is mounted to a moving assembly or gantry for moving the pump and dispenser assembly along three mutually orthogonal axes (X, Y, Z) using servomotors controlled by a computer system or controller. To dispense a dot of liquid on a circuit board or other substrate at a desired location, the pump and dispenser assembly is moved along the co-planar horizontal X and Y axes until it is located over the desired location. The pump and dispenser assembly is then lowered along the perpendicularly oriented vertical Z axis until a nozzle/needle of the pump and dispenser assembly is at an appropriate dispensing height over the substrate. The pump and dispenser assembly dispenses a dot of liquid, is then raised along the Z axis, moved along the X and Y axes to a new location, and is lowered along the Z axis to dispense the next liquid dot. For applications such as encapsulation or underfilling as described above, the pump and dispenser assembly is typically controlled to dispense lines of material as the pump and dispenser are moved in the X and Y axes along the desired path of the lines.
The production rate of such dispensing systems, in some cases, may be limited by the rate at which a particular dispense pump assembly can accurately and controllably dispense dots or lines of material. In other cases, the production rate of such systems may be limited by the rate at which parts can be loaded into and out of the machine. In still other cases, the production rate of such systems may be limited by process requirements, such as the time required to heat a substrate to a particular temperature, or the time required for a dispensed material to flow, as in underfill applications. In all cases and applications, there is some limit to the throughput capability of a single dispense system.
During the manufacture of integrated circuits, production requirements often exceed the throughput capabilities of a single dispensing system. To overcome the throughput limitations of a single dispensing system, various strategies are applied to improve the production process.